Cardiac remodeling in middle-aged endurance athletes: relation between signal-averaged electrocardiogram and LV mass
Background: The relationship between structural and electrical remodeling in the heart, particularly after long-standing endurance training, remains unclear. Signal-averaged electrocardiogram (SAECG) may provide a more sensitive method to evaluate cardiac remodeling than a 12-lead electrocardiogram (ECG). Accurate measures of electrical function (SAECG filtered QRS duration (fQRSd) and late potentials (LP) and left-ventricular mass (cardiac magnetic resonance, CMR) can allow an assessment of structural and electrical remodeling. Methods: Endurance athletes (45-65 years old, >10 years of endurance sport), screened to exclude cardiac disease, had standardized 12-lead ECG, SAECG, resting echocardiogram (ECHO), and CMR performed. SAECG fQRSd was correlated with QRS duration on the 12-lead ECG, and ECHO and CMR-derived left ventricular (LV) mass. Results: Participants (n=82, 67% male, mean age: 54±6 years, mean VO2max: 50±7 ml/kg/min) had a CMR-derived LV mass of 118±28 g/m2 and a fQRSd of 112±8 ms (46% had abnormal fQRSd (>114 msec), and 51% met clinical threshold for abnormal SAECG). fQRSd was positively correlated with the 12-lead ECG QRS duration (r=0.83), ECHO-derived LV mass (r=0.60), CMR-derived LV mass (r=0.58) and LV end-diastolic volume (r=0.63, p<0.001 for all). fQRSd had higher correlations with ECHO and CMR-derived LV mass than 12-lead ECG (p<0.0008 and p<0.0005, respectively). Conclusion: In a healthy cohort of middle-aged endurance athletes, the SAECG is often abnormal by conventional criteria, and is correlated with structural remodeling, but CMR evaluation does not indicate pathologic structural remodeling. SAECG fQRSd is superior to the 12-lead ECG for the electrocardiographic evaluation of LV mass.